The fields of application concerned are sub-surface analysis devices of confocal character, the conveyed signals being able to be in particular in the field of imaging and/or the spectroscopy depending on the excitation source(s) and the detection means used. The confocal character results from the use of the same fibre to convey the excitation signal and the back-emitted signal, and a very reduced spatial dimension of the fibre. These may be in-situ biological analyses, on people or animals, external for example in the field of dermatology, or internal and accessible with the help of an endoscope operating channel into which the bundle of optical fibres and the optical head can be introduced. They may also be cell analyses carried out ex vivo on samples. Furthermore, the optical head can also be used for the analysis of the interior of a manufactured device.
The medical fields concerned in the present case are gastroenterology, pneumology, gynaecology, urology, ORL, dermatology, opthalmology, cardiology and neurology.
The means of signal analysis and processing provided on the proximal end side of the bundle of optical fibres allow the restoration of an image or a graph that can be interpreted by a user.
Document WO 03/056379 is known, describing a miniaturized optical head envisaged for equipping the distal end of an image guide. This optical head consists of an optics-holder tube of circular section within which are introduced, on one side, the distal terminal part of the image guide and, on the other, optical focusing means. The optical means comprise lenses arranged in extra-focal planes. The lenses are arranged so as to optimize the signal-to-noise ratio by minimizing the stray reflection at the output of the image guide, by optimizing the return coupling level and by optimizing the transmission of the head assembly. The subject of the present invention is an optical head offering a good image quality for fluorescence systems in particular.
The document by A. R. Rouse, A. Kano, J. A. Udovich, S. M. Kroto and A. F. Gmitro, “Design and demonstration of a miniature catheter for a confocal microendoscope”, Applied Optics, vol. 43, no 31, pp. 5763-5771, 2004, is also known. This document describes an optical head which is located in the distal part of an image guide. This optical head has the following characteristics:                Magnification=1.6, which makes very little difference and does not allow a large lateral resolution to be obtained;        Numerical aperture on the tissue=0.46, which is a drawback for the collection of the photons from the fluorescence of the tissue; the sensitivity cannot be very high with such an optical solution;        Diameter of the head=3 mm;        Length of the head=13 mm, which is compatible with the passage through the operating channel of an endoscope;        Point axial resolution=10 μm, which is a fairly large value for an optical head comprising a relatively complicated optical design;        Planar axial resolution=25 μm (i.e. for an entire image field), which is a significant value for an optical head comprising a complicated optical design;        Lateral resolution=3 μm, fairly degraded for an optical head of this type.        
The optical head according to the prior art does not have optical performance values that allow it to be ranked as an optical head with high resolution and high sensitivity. Moreover, the Rouse document describes a direct line-by-line scanning system and not a point-by-point scanning system injecting the optical beam in turn into each of the optical fibres constituting the image guide.